Poly(hydroxyalkanoic acid) (PHA) polymers such as poly(lactic acid) (PLA) may be polymerized from renewable sources rather than petroleum and are compostable. They have a broad range of industrial and biomedical applications. However, physical limitations such as brittleness and slow crystallization may prevent easy injection molding of PHAs into articles that have an acceptable degree of toughness for many applications. Extruded amorphous sheeting may also be too brittle for handling in continuous moving equipment without breakage.
Modifiers for PHAs allow PHA compositions to be easily melt-processed into a variety of articles with an acceptable level of toughness are known. See, e.g., JP09-316310A (PLA composition comprising modified olefin compounds), U.S. Pat. Nos. 7,268,190 and 7,381,772 and US patent applications 2007/0213466 and 2008/0027178 (PHA compositions toughened with ethylene ester copolymers containing glycidyl groups such as ethylene/butyl acrylate/glycidyl methacrylate), JP09-12844 (polyester composition composed of polyether ester amide and a modified vinyl polymer), WO2007127303 (blend comprising PLA and at least 5 weight % of ethylene/unsaturated ester copolymer having an unsaturated ester comonomer content of at least about 30, modified ethylene/unsaturated ester copolymer, polyetheramide block copolymer; propylene/ethylene copolymer comprising, or styrenic block copolymer), and WO2008078413 (a biodegradable polyester composition obtained by melt-mixing a biodegradable polyester containing not less than 70% by mole of an α- and/or β-hydroxycarboxylic acid unit, a polyether/olefin block copolymer resin or a polyether ester amide copolymer resin, a (meth)acrylate compound, and a peroxide).
A fabricated article made from a polymeric material may become statically charged, and the surface may attract and hold charged particles such as dust in the air. In some cases an article may become damaged and/or otherwise devalued by the adhesion of electrostatically charged species. In other cases, such as in the packaging of powders, the powder may adhere to the packaging material. In addition to electrostatic adhesion, the buildup of excessive static charge on articles may result in damage to the article and/or its surroundings due to sparks and other rapid electrostatic discharges.
To prevent adhesion of charged particles, various approaches for preventing surface static charge buildup have been disclosed. For example, an antistatic agent or an antistatic polymer may be applied to the surface, or diffuse from the bulk composition to the surface, of an article as a way of preventing build-up of static charge on an article. See, for example, JP02-28919B, JP61-44646A, and JP10-193495A.
Use of surface-applied antistatic agents may introduce potential contamination of materials that come in contact with the surface-applied antistatic agent. Other drawbacks include situations wherein the applied film is inadequate in mechanical properties and could be easily damaged, has poor water resistance, or becomes tacky due to absorption of water. Attempts have been made to provide an antistatic polymer layer not as a surface layer, but as an inner layer with another polymer layer on the surface of the material.
Alternatively, antistatic agents may be incorporated into the composition of a molded article. However, materials that come in contact with the composition may become contaminated due to bleeding of the antistatic agent out of the composition and/or the antistatic effect may deteriorate with time. Incorporation of a low-molecular ionic surfactant such as an alkylsulfonic acid salt or an alkylbenzenesulfonic acid salt into a polymer is known as an internal addition process. However, surfactants may degrade the PHA resin.
“Permanent”, non-diffusing antistatic agents avoid many of these problems. High molecular weight or polymeric antistatic materials have been developed to provide permanent antistatic agents. For example, a composition comprising thermoplastic polyurethane, a thermoplastic polyester (the polyester is a polylactone), and a quaternary ammonium compound is disclosed (e.g., U.S. Pat. No. 5,863,466).
Permanent antistatic agents include “inherently dissipative polymers”. Polyether ester amides are known to promote antistaticity. However, using polyether ester amides as modifiers of other thermoplastic resins may cause laminar peeling and the production of a molded article having desirable mechanical properties may difficult because of incompatibility.
A composition has been disclosed which comprises (A) a thermoplastic polymer and (B) an antistatic agent wherein a refractive index difference between (A) and (B) is not more than 0.02 (e.g., US 2005/0049360). See also U.S. Pat. No. 6,268,030 (a composition composed of polytetramethylene terephthalate, polyether ester amide, an alkaline metal and a modified polyolefin) and JP2006-131798 (PLA-based composition comprising PLA, a polyetheresteramide polymer and/or a block polymer having a structure in which a polyolefin block and a block of a polymer containing a polyoxyethylene chain are mutually bonded repeatedly).
It is desirable to provide toughened PLA compositions with good antistatic properties.